The Gameboy game can be very confusing, and you may need direction.
PoJo and other PokeMasters have compiled many tips to help you complete your journey.

Your quest: Collect all 150 Pokémon, just like Ash,
using your own Pokémon to capture others. Along the way, several skilled trainers, such
as Gary, and many minor trainers will challenge you to Pokémon duels. To win the game,
you must defeat them all.

Remember, Pokémon are not ordinary creatures. To collect all 150, you'll need
to train captured Pokémon so they evolve. For instance, a captured Caterpie will evolve
into a Metapod, which will then turn into a Butterfree. Each transformation adds more
power to the Pokémon  giving you more power to defeat and capture other Pokémon.

Also keep in mind that some Pokémon are rare and won't be found in your game.
The Red and Blue versions of the game each carry their own variety of Pokémon to defeat,
collect, and train. To get all 150, trade Pokémon with your friends using the Game Boy
Link Cable, which allows the transfer of Pokémon between Game Paks.